Nowadays the lithium-ion batteries used in mobile phones and notebook computers often have lithium cobalt oxide as the cathode material. Lithium cobalt oxide has an initial discharge capacity of 140˜145 mAh/g and has a good cycling performance. It has been widely used as the cathode material for lithium ion batteries since 1992. After years of continuous improvement, lithium cobalt oxide cathode material can have a compact density that reaches 3.6˜3.8 g/cm3, which meets the per unit volume of capacity requirement for the laptop batteries. However, due to shortage of cobalt, lithium cobalt oxide material is expensive. It also suffers from deficiencies including difficulty in further improving capacity, poor safety performance, etc. In order to find high performance, low price lithium-ion battery cathode materials, researchers domestically and abroad conducted extensive research in the preparation of cathode materials such as lithium manganese oxide, lithium nickel oxide, etc. Lithium manganese oxide has a relatively low discharge capacity. Its cycling performance, especially that under high temperature, is relatively poor, which greatly restricted its application. Currently lithium manganese oxide is mainly used in small power batteries. Synthesis of lithium nickel oxide is relatively difficult, which are still in the development stage.
Lithium nickel cobalt manganese oxide multi-element cathode materials (hereinafter referred to the “multi-element cathode material”) is a new high capacity lithium-ion battery cathode material. This material has good safety performance, lower price, good compatibility with the electrolyte, and good cycling performance. However, the synthesis of this material is rather difficult. The material produced are relatively unstable. Its tap density and compact density are much lower than that of lithium cobalt oxide, which hinders the practical application of this material. In recent years, after extensive research, the preparation of multi-element cathode material has made great progress, having developed polycrystalline (mostly spherical) nickel-cobalt-manganese multi-element cathode material. Observation under the microscope shows that the particle of the multi-element cathode material is made from a number of tiny particles agglomerated together. The tap density of this multi-element cathode materials is up to 2.0˜2.5 g/cm3. Its initial discharge capacity is 140˜145 mAh/g. The current consensus is that the polycrystalline particles is the best structure for the nickel-cobalt-manganese multi-element cathode material. Multi-element lithium nickel cobalt manganese oxide cathode materials produced by domestic and foreign manufacturers are all in forms of polycrystalline particles. However, the preparation of polycrystalline multi-element lithium nickel cobalt manganese is complex. Although the resulting material has a relatively high tap density (up to about 2.4 g/cm) and a compact density of up to 3.2˜3.4 g/cm3, it is difficult to further improve upon. Furthermore, the polycrystalline particle made from a number of small particles has difficulties to maintain an uniform particle diameter, the particle size distribution is rather broad. During manufacturing process of battery cathode, the small particles may fall off from the polycrystalline particle, which leads to a lower stability of the product. In addition, spherical polycrystalline particles has relatively large absorption of moisture, which affects the performance of the product during operation. Therefore, the polycrystalline nickel-cobalt-manganese multi-element cathode material is difficult to find practical applications in high end products (such as laptop computer batteries, etc.).